1. Field of the Invention
The present invention relates to a helical antenna for portable radio devices, formed by means of a coated conductive layer around an insulator, and in which a coil component and mounting component are integrally formed, as well as to its method of manufacture.
2. Description of Related Art
Helical antennae with spirally shaped coil elements are widely used in portable radio devices such as portable telephones.
An example of a coil which is used in such conventional helical antennae is depicted in FIG. 13.
As shown in the figure, a helical antenna 100 comprises a cover component 101, a coil component 102, and a mounting component 103, with the coil component 102 housed inside the cover component 101, and the mounting component, which is used to join the antenna to the radio device, located at the bottom end.
FIG. 14 shows an example of a coil with another structure 200 used in helical antennae, which are fabricated by providing a spiral groove 202 around the sides of an insulated, columnar body 201, and by then providing a plating layer 203 on the concave surface of the spiral groove 202. The spiral antenna 200 is alternatively fabricated by forming a plating layer 203 on the insulated, columnar body 201 having the spiral groove 202, either in its entirety or on the entire side surface thereof; finally removing the excess plating layer 203 on the outermost layer of the side surface of the insulated, columnar body 201 by grinding it or the like; and leaving the plating layer 203 on the concave surface of the spiral groove 202.
The method for manufacturing a coil element, which is noted in Japanese Laid-Open Patent Application 7-302716, is described below with reference to FIG. 15.
As shown in FIG. 15a, 302 is a mounting component of, an insulated cylindrical main body 301. A spiral groove 303 is provided, as shown in FIG. 15b, around the outer peripheral side surface of the main body 301. A conductive layer 307 consisting of a metal is then allowed to adhere by means of plating or the like to the entire surface of the main body 301 and the mounting component 302, resulting in the state depicted in FIG. 15c. The outer peripheral side surface of the main body 301 is then machined with a lathe or the like, and the upper surface of the main body 301 is ground.
When this is done, the conductive layer 307 that adheres to the bottom of the main body 301 and inside the groove 303, and that has been formed on the surface of the mounting component 302, is left, and the conductive layer 307 adhering to the outer peripheral side surface of the main body 301 is removed by machining. This results in the manufacture of the coil element depicted in FIG. 15d, which is furnished with a coil component 304 formed by the conductive layer 307 in the groove 303.
The helical antenna depicted in FIG. 13, however, suffers from the drawbacks of higher manufacturing costs and irregular electrical properties because it is constructed by assembling a coil component, cover component, and mounting component with individual parts.
When electrical power is applied to the spiral antenna on which a spiral groove has been formed, as shown in FIG. 14, electrical power can be supplied only by soldering a lead to the plating layer 203 formed in the groove, resulting in the inconvenience of the working procedures needed for the supply of electrical power.
As shown in FIG. 15, the device is integrated with the mounting component, but the device depicted in FIG. 15 suffers from drawbacks in that the thinness and the high degree of hardness of the plating layer result in poor workability, causing the plating layer to be broken during the machining process, or burrs are produced in the plating layer as a result of the machining, and so forth, so that irregularities are produced in the electrical properties of the coil element. Particularly when a cover is molded over the coil element, the risk of burrs adhering to undesirable parts during molding results in the deterioration of the electrical properties and quality.
In addition, when a helical antenna is used in a portable telephone or portable radio device, such devices are frequently used in poor environments involving rugged use and exposure to wind and rain, with considerable external force exerted on the antenna component. When conventional helical antennae are mounted on radio device main bodies, problems include insufficient mechanical strength and a poor water-proof mechanism.
Furthermore, when portable radio devices are dropped or the like, and when force is obliquely exerted on the antenna and the like, there are problems in that the impact received by the antenna is transmitted as such to the base plate of the radio device main body, damaging the base plate.